Conveyer control



CONVEYER CONTROL Filed Aug. 25, 1941 Snventors Patented Apr. 6, 1943CONVEYER. CONTROL John C. Owens, Grand Blanc, and Raymond A. Schomer,Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application August 23, 1941, Serial No. 408,062

6 Claims.

The 'present invention relates generally to speed regulating means andmore particularly to a simple speed regulating means for conveyers whichinsures that a preselected number of objects supported in equally spacedrelation on the conveyer will pass assembly stations in any preselectedconstant interval of time.

In manufacturing plants where long main conveyers are used for movingsubassemblies and branch conveyers are used for moving parts it isnecessary that the parts and subassemblies arrive at assembly stationssimultaneously and at regular intervals so that the necessary assemblyoperations may be completed during the interval of movement of thesubassemblies and parts past the assembly stations. On account of thelength and weight of these conveyers and non-uniform loading thereon asassembly progresses, wear and slack develops in the conveyer, whichcauses hunting of the many driving motors required to operate theconveyers and at times causes damage to the conveyer and driving meanstherefor.

The principal `object of the present invention is the provision ofsimple drive and control means for a conveyer which is controlledjointly by the conveyer and time controlled means operating in timedrelation with the conveyer for frequently regulating the power suppliedto the conveyer driving motors to maintain constant uniform linearmovement of the conveyer.

The means by which the above object is accomplished, together with otherfeatures of the invention, will be better understood by referring totlie following detailed description of the invention and the singledrawing illustrating the invention in diagrammatic form.

Referring now to the drawing, an endless conveyer is shown at I. whichmay be of the belt or chain type, and which has a number of dogs 3 fixedat equally spaced points thereon for locating objects to be conveyedfrom one position to another. The conveyer is supported on pulleys orsprockets. two of which are shown at 5, driven at any desiredpreselected speed by means of the gears 1 and 9 and direct currentmotors Mi and M2.

A motor generator exciter power source is provided for^r energizing themotors which comprises a direct current generator G, a direct currentexciter EX and a three phase induction motor 1M for driving the exciterand generator. The induction motor is shown connected to a commercialthree phase power line L the frequency of which is accurately controlledby any well known time controlled means. The exciter EX furnishesexcitation current for the generator G and motors MI and M2. Thearmature Il of the exciter is shown connected in parallel with theexciter excitation winding i3 and the excitation windings I5 and i1 ofthe motors Mi and M2 and also the excitation winding i9 of the generatorG, suitable excitation varying means comprising the field rheostats I, Mand D being shown connected in series with the gen- `time controlledswitches IS, HS and DS to adjust the generator excitation current atfrequent intervals in order to vary the power supplied to the conveyerdriving motors and thereby maintain constant linear speed of theconveyer.

'I'he relays IR and DR as shown include an actuating winding, a movablearmature having con- ,tacts fixed thereon and two pairs of fixedcontacts` The upper pair of fixed contacts of the relay IR are shownconnected across the rheostat I and the lower pair of fixed contacts areholding contacts, t'o be referred to later. The contact arrangement ofthe relay IR, as shown, is such that the relay armature is attracted andmoved y upward from the normal position upon energization of the relaywinding to cause both pairs of fixed contacts to be bridged by thearmature contacts. As the upper pair of fixed contacts are shownconnected across the rheostat I, when these contacts are bridged therheostat is shunted to increase the generator excitation and thereforeincrease the power output to themotors Mil and M2 and the speed thereof.The rheostat I and relayIR, therefore, serve as driving motor speedincreasing means. The upper pair of con- .tacts of the relay DR. areshown connected across erator excitation circuit to decrease thegenerator excitation current and therefore decrease the power output tothe motors MI and M2 and the speed thereof. The rheostat D and relay DR,therefore, serve as driving motor speed decreasing means.

Each of the time controlled switches IS, HS

and DS includes a cam disc xed to a camshaft 21, a pivoted cam followercontact arm and a fixed contact contactable by the contact arm. Thecamshaft 21 is rotated at constant speed in the direction shown by thearrow through gears 29 and 3| by a. synchronous driving motor shown atSM. The synchronous motor SM is shown connected across the secondary ofa transformer T, the primary of which is connected to one phase of thepower line L. As the frequency of the power line, as previouslymentioned, is maintained constant by time controlled means, the speed ofthe synchronous motor and the cam switches driven thereby will beconstant and therefore constitute time controlled switching means.

The gear ratio of the gears 29 and 3| is selected so that the camshaft21 is rotated in timed relation with the conveyer in such manner thatone revolution of the shaft corresponds to uniform linear movement ofthe conveyer equal to the distance between successive dogs 3 equallyspaced on the conveyer I. The cam discs are so formed and fixed on thecamshaft 21 that, upon rotation of the camshaft through one revolution,the cyclic sequence of operation of the switches IS, HS and DS from theposition in which they are shown is as follows: (l) switch IS closes;(2) switch IS opens; (3) switch HS opens; (4) switch DS closes; (5)switch HS closes; (6) switch DS opens; (7) switch HS opens. As will besubsequently explained, the switch IS controls energization of relay IRand therefore is part of the driving motor speed increasing means. Theswitches DS and HS serve jointly to control energization andde-energization of the relay DR and therefore are part of the drivingmotor speed decreasing means, the switch HS serving as a holding switch.

The limit switch LS is provided with a pivoted contact arm movable intocontact with a fixed contact located adjacent thereto. I'he limit switchis located adjacent the conveyer and the control arm is formed as shownso that it will be struck and moved momentarily into contact with thefixed contact by each of the dogs 3 on the conveyer.

The control and holding circuit connections interconnecting the abovedescribed relay windings and switches, whereby the generator'excitationis automatically adjusted at frequent intervals to maintain the speed ofthe conveyer constant, will now be described. The lower terminals ofeach of the relay actuating windings are shown connected by conductors33 and 35 to the upper terminal of the secondary winding of thetransformer T. The lower terminal of the transformer secondary windingis connected to the fixed contact of the limit switch LS by a conductor31. The contact arm of the limit switch is connected by a conductor 33to the left holding contact of the relay IR, and conductors 4I and 43are connected, respectively, between the conductor 33 and the fixedcontacts of the speed increasing and decreasing cam switches IS and DS.The contact arm of the switch IS is connected by a conductor 45 to theupper terminal of the winding of relay IR, and the contact arm of theswitch DS is connected to the upper terminal of the winding of relay DRand also the right holding contact of this relay by conductors 41 and4B. The right holding contact of relay IR is connected by a conductor 5|to the fixed contact of the cam holding switch HS and a conductor 53 isconnected between the conductor 5I and the lower terminal of thetransformer secondary winding. rThe left holding contact of relay DR isconnected by a conductor 55 to the Contact arm of the holding switch HS.

The operation of the combined conveyer drive and control system is asfollows: With the motor generator exciter power source in operation andthe conveyer normally loaded, the rheostats M, I and D are adjusted tocause the conveyer I to be driven by the driving motors at the desiredpreselected value of speed. When the induction motor is energized fromthe power line L, the transformer T and the synchronous motor SM willlikewise be energized and will operate at synchronous speed to drive theshaft 21 at constant speed in timed relation with the speed of theconveyer, as previously explained. With the cam switches IS, HS and DSin the positions shown, that is, with the switches IS and DS open andthe holding switch HS closed, should the limit switch LS be momentarilyclosed by passage of one of the conveyer dogs 3, neither of the windingsof the relays IR or DR will be energized as each of the switches IS andDS is open and is connected in series relation between the limit switchand each of the relay windings. 'I'he relay armatures will, accordingly,remain in the normal position as shown, with the rheostat D shunted out4by the bridged upper xed contacts of the relay DR, and the rheostat Mand rheostat I will be connected in series relation with the generatorexcitation winding to limit the current therein such that the powersupplied to the driving motors is of the proper value to maintain thespeed of the conveyer at the correct preselected value.

Should the speed of the conveyer decrease slightly below the correctvalue between the passage of successive conveyer dogs 3 the limit switchwill be momentarily closed late by one of the dogs 3, that is, after thecam switch IS is closed. With the switches IS and LS closedsimultaneously the winding of the speed increasing relay m will beconnected across the transformer secondary winding and energized throughthe closed contacts of these switches and conductors 31, 39, 4I, 45, 35and 33. The armature of the relay IR will, accordingly, be attracted andmoved upward and the contacts thereon will simultaneously bridge bothpairs of fixed relay contacts. Bridging of the upper pair of relaycontacts shunts out the rheostat I to increase the excitation current inthe generator field winding I9 to increase the power output of thegenerator G to the conveyer driving motors MI and M2 to increase thespeed of these motors and the conveyer I. Bridging of the holdingcontacts, that is, the lower fixed pair of contacts of the relay IR,establishes a holding circuit to the relay winding before opening of thelimit switch LS through the bridged relay holding contacts and closedcontacts of switch IS and conductors 53, 5 I, 39, 4I, 45, 35 and 33 tomaintain the relay winding energized and rheostat I shunted until theswitch IS is again opened by rotation of its cam through an angle which,as shown, is less than 360. This angle is determined by the length ofthe convefyer, the load thereon and operating and regulatingcharacteristics of the generator G and motors MI and M2 and theresistance of the rheostat I to obtain prompt adjustment of the speed ofthe driving motors.

Upon a slight increase in the speed of the conveyer above that of thepreselected correct value the limit switch will be momentarily closedearly, that is, upon closure of the speed decreasing cam switch DS.Simultaneous closure of the switches LS and DS causes the winding of thespeed decreasing relay DR. to^be connected across the secondary of thetransformer T vand energized through the closed contacts of theseswitches and conductors 31, 43, 41, 49 and 33. The amature of the relayDR will, accordingly, be attracted and moved upward and the contactsthereon will bridge the relay holding contacts and open the upper pairof fixed contacts. Bridging of the holding contacts establishes aholding circuit to the relay winding before the limit switch opensthrough the bridged holding contacts of the relay and closed contacts ofthe holding switch HS and conductors 53, 5I, 55, 41, 49 and 33. Theholding switch HS closes slightly before the limit switch LS and thespeed decreasing switch DS open, and remains closed until opened byrotation of its cam disc through an angle suitable to cause a promptdecrease in the speed of the driving motors and conveyer to the correctspeed. The angle necessary to maintain the holding switch closed is alsodetermined by the operating characteristics of the generator and motorsand the length of the conveyer, load thereon and the resistance of therheostat D.

With the above described generator excitation regulating means the speedincreasing relay is initially energized by late momentary closure of thelimit switch LS when the speed increasing switch IS is also closed, andthis relay is maintained energized as long as the relay holding contactsare bridged and the speed increasing switch IS is closed, which is lessthan one revolution ofthe cam disc operating this switch. The resistanceof the rheostat I may be adjusted so that during the interval it isshunted out of the generator excitation circuit by the relay IR theresulting increase in generator -power output to the motors issufficient to increase the speed of the motors MI and M2 and conveyer Ito the correct speed when the switch IS is opened.

Early momentary closure of the limit switch LS, that is, when both thespeed decreasing switch DS and holding switch HS are closed causes thespeed decreasing relay to be initially energized, and this relay ismaintained energized as long as the holding contacts of this relay arebridged and the holding switch HS is closed, which is likewise less thanone revolution of the cam disc operating this switch. The resistance ofthe rheostat I) is adjusted so that during the interval it is insertedin the generator the reduction in the excitation current and theresulting decrease in the power output of the generator to the motors issuflicient to cause the speed of the motors MI and M2 and conveyer I tobe increased to the correct speed value when the holding switch HS isopened. The rheostat M in series with the rheostats I and D is adjustedinitially to cause the conveyer to be driven at the proper value ofspeed selected.

Closure of the limit switch at times other than those described above,that is, when the conveyer is operating at the correct speed, causes nochange in the generator excitation and output to the motors andtherefore no correction in the speed thereof.

The above described conveyer drive and control system provides, afrequent periodic adjustment of the power supplied to the conveyerdriving motors at substantially constant time intervals when theconveyer speed varies slightly from a preselected constant value ofspeed. It will be evident that the speed of the conveyer may be changedto any preselected value by changing the gear ratio between the drivingmotors MI and M2 and conveyer I and also by changing the ratio betweenthe synchronous motor SM arid the shaft 21 operating the cam operatedswitches retaining the same relation of timing between the conveyer Iand camshaft 21 as described above.

The direct current power source and driving motors and adjustablerheostats allow slight adjustments to be made in the speed of the motorsand give satisfactory and prompt speed and output regulation upon theinsertion or shunting out of these rheostats by the relays, and the timecontrolled means, or switches driven by the synchronous motor, providea. constant reference speed for the speed of the conveyer and motors.The regulating means operated jointly by the conveyer dogs and timecontrolled means operates in a highly satisfactory manner withoutadjustment for long periods of time and eifectively prevents hunting ofthe driving motors and damage to the conveyer and mechanical drivingmeans therefor.

It will be evident that we have provided conveyer speed control meanswhich is operated jointly by means operated at frequent andsubstantially constant time intervals by the conveyer and timecontrolled means operated at constant time intervals and in timedrelation with the means operated by the conveyer so that any slightdeviation in the speed of the conveyer with respect to the timecontrolled means will cause a prompt adjustment in the temporary speedof the conveyer such that it will run at an average value of speed equalto that of the time controlled means.

' We claim: y

1. A constant speed drive and control system comprising a conveyerhaving a multiplicity of equally spaced locating means fixed thereon forlocating objects to be conveyed, motors for driving the conveyer, asource of power for the motors, output regulating means for said powersource serving as speed regulating means for said motors, and controlmeans for said output regulating means comprising a plurality ofswitches interconnected with said output regulating means, one ofsaidswitches being operable intermittently by said conveyer locatingmeans and time controlled means for operating other of said switches atconstant speed in timed sequence relation with said conveyer operatedswitch so that said output regulating means is controlled jointly bysaid switches at frequent intervals to maintain the speed of theconveyer constant.

2. In a constant speed drive and control system comprising a conveyerhavinga plurality of equally spaced locating means fixed thereto forpositioning objects to be conveyed, a. plurality of motors for drivingthe conveyer, a generator supplying power to the motors, generatorexcitation varying means to vary the generator output to the motors andtherefore the speed thereof, and control means for said excitationvarying means comprising relays for controlling the excitation varyingmeans and switching means interconnected with the relays for controllingenergization and deenergization of said relays, said switching meanscomprising a limit switch operated intermittently by said conveyerlocating means and time controlled means for driving other switches intimed operating sequence relation with the conveyer to cause frequentintermittent operation of said relays only upon a slight deviation ofthe speed of the conveyer locating means with reference to the speed ofthe time controlled switches in order to cause frequent periodiccorrection in the speed of the conveyer.

3. In a constant speed drive and control system comprising a conveyerhaving locating means fixed thereon at equally spaced intervals tolocate objects to be conveyed, motors for driving the conveyer, a sourceof power for said motors comprising a motor generator exciter set forsupplying power and excitation current to both the generator and themotors driving the conveyer, generator excitation increasing anddecreasing means for increasing or decreasing the power supplied to thedriving motors by the generator to vary the speed of the motors thereofand control means for said generator excitation increasing anddecreasing means comprising a plurality of switches interconnected withsaid excitation increasing and decreasing means, time controlled meanscomprising a synchronous motor for operating certain of said switches intimed sequence relation with the conveyer locating means and a switchoperated momentarily by each of said locating means so that saidexcitation increasing or decreasing means is operated at frequentintervals to maintain the speed of the conveyer equal to the speed ofthe time controlled means.

4. In a constant speed drive and control system comprising a conveyer, aplurality of direct current motors for driving the conveyer, dogs fixedat equally spaced intervals on the conveyer, a source of power for themotors comprising a direct current generator, a direct current exciterand an alternating current motor connected to a constant frequency powersource for driving the generator and exciter, power connections betweenthe generator and motors, generator and motor excitation circuitsconnected to the exciter, rheostats in said generator excitationcircuit, relays or inserting or shunting said rheostats to vary theexcitation of the generator to vary the power output thereof to thedriving motors in order to vary the speed of the driving motors, aconstant frequency control circuit including a synchronous motor,switches operated in a definite cyclic sequence thereby and a limitswitch operable momentarily by each conveyer dog i'or each cycle ofoperation of said nrst named switch to complete a connection throughcertain of said switches and relays upon slight differences in the speedof the conveyer with respect to the synchronous motor in order tocontrol the relays and cause an increase or decrease in the speed of thedriving motors at trequent intervals to prevent hunting of the motorsand to cause the speed of the conveyer to be maintained constant.

5. A constant speed drive and control system comprising a conveyer,motors for driving the conveyer at substantially constant speed, a powersource for the motors; output regulating means for the power sourceserving as speed regulating means for the motors, control means ior theoutput regulating means comprising a plurality of switches, meansequally spaced on the conveyer to operate one of said switches atfrequent equally spaced time intervals determined by the speed of theconveyer and time controlled means for operating the other switches atconstant time intervalsin timed sequence relation with the switchoperated by the means on the conveyer so that the output regulatingmeans is controlled jointly by said switches to cause the average speedof the conveyer to be equal to that of the time controlled means.

6. A constant speed drive and control system comprising a travelingconveyer, motors for driving the conveyer at substantially constantspeed, a power source connected to said motors, output regulating meansfor said power source to regulate the speed of the motors, control meansior said regulating means comprising interconnected switches, one ofsaid switches serving as a limit switch, means arranged on said conveyerand positioned to operate the limit switch at equally spaced intervalsof conveyer travel, and time controlled means for operating the otherswitches in timed sequence relation with the means operating the limitswitch so that the output regulating means is controlled at frequentintervals by the limit switch and switches interconnected therewith anddriven by the time controlled means to cause the conveyer to be drivenat constant speed.

JOHN C. OWENS. RAYMOND A. SCHOMER.

